Abstract
This study was carried out to evaluate the effects of dietary trace mineral levels and sources on egg quality parameters of second-cycle semi-heavy layers. A number of 360 72-week-old layers were submitted to forced molting. Upon return of lay (83 weeks of age), birds were distributed according to a completely randomized experimental design of six treatments with six replicates of 10 birds each. The control treatment consisted of 0.10% dietary supplementation of trace minerals from inorganic sources, which was proportionally replaced by five levels (110, 100, 90, 80, 70%) of an organic trace mineral supplement containing 30, 30, 40, 6, 0.61, and 0.3 g/kg product of Zn, Fe, Mn, Cu, I, and Se, respectively. All diets contained equal protein, energy, and amino acid levels. Every 28 days of the experimental period (112 days) four eggs per replicate were collected for egg quality evaluation. The following parameters were evaluated: specific gravity, yolk, albumen and eggshell percentages, yolk index, Haugh units, and eggshell thickness and breaking strength. One sample per replicate, consisting of the pool of the yolks of three eggs collected at the end of each experimental period, was used to assess protein and mineral (Ca, P, Cu, Fe, Mn, and Zn) contents. The results were submitted to ANOVA, and means to the test of Tukey at 5% significance level. The evaluated trace mineral levels and sources did not influence any of the studied egg quality parameters. It was concluded that reducing organic trace mineral supplementation in up to 70% relative to 100% inorganic trace mineral supplementation does not affect egg parameters and therefore, can be applied to the diet of semi-heavy layers in their second cycle of lay.
Highlights
Forced molting of layers has been increasingly used in Brazil as it results in high egg production and large eggs, which demands the adjustment of dietary nutritional levels
Despite the intensive use of a second laying cycle, there is little information on the nutritional levels recommended for layers in this phase; in general, the nutritional requirements of layers at the end of the first cycle of lay are applied with slight reduction of the nutritional levels
The studied trace minerals levels, including those obtained by organic sources, may have been higher than those required to optimize egg quality
Summary
Forced molting of layers has been increasingly used in Brazil as it results in high egg production and large eggs, which demands the adjustment of dietary nutritional levels. Improving mineral bioavailability by using organic sources may be an option to adjust nutritional levels. Both large and trace minerals added to poultry diets traditionally derive from inorganic sources, such as oxides, sulfates, chlorides, carbonates, and phosphates. Excessive levels of minerals, such as Zn, Cu, Fe, and Mn, have been used to prevent deficiencies (Bertechini, 2003) caused by possible interactions among these minerals and other dietary components, rendering them unavailable to the bird's digestive system (Mabe et al, 2003).
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